1. Field of the Invention
The present invention relates to a communication control method suitably applied to a local area network (LAN) configured of a plurality of devices for transmitting various information by radio signals, for example, and a transmission unit using such a control method.
2. Description of the Related Art
In a conventional local area network constructed to transmit data between a plurality of devices such as various video devices or between a personal computer and peripheral devices thereof within a comparatively small area such as a residential house, an office or the like, upon assembling a local area network, the devices are sometimes connected with a radio signal transceiver (radio transmission unit) connected to each device to permit data transmission by radio without directly connecting the devices by some signal lines.
In the case where a local area network is constructed by radio transmission, the respective component devices are not required to be connected directly with signal lines or the like and therefore the system configuration can be simplified.
Assume that a local area network is constructed by a plurality of radio transmission units. In the case where signals are transmitted at the same time from a plurality of the transmission units using the same transmission band, there is a possibility that a transmission error is liable to occur. Therefore, each communication between the transmission units in the network is required to be accessed and controlled by some method.
In a conventionally well-known access control method such as a small-scale radio network, for example, the communication between the transmission units (nodes) within the network is one-dimensionally managed by a transmission unit (root node) arranged at the central portion of a star-connected configuration. A conventional general method for avoiding a conflict in such a network is a band reservation method in which a band is reserved for each transmission line regardless of the presence or absence of transmission data and the transmission is conducted in the reserved band. With this method, however, it is necessary to secure a band of the transmission line even when the data to be transmitted is lacking, and the network resources are used wastefully and the problem of very low efficiency is posed.
An access method that has solved this problem is the communication conducted by polling control within a network. In this method, one arbitrary transmission unit in the network is determined as a control station (root node) which transmits a control signal for polling the other nodes sequentially in the network, and a signal is transmitted from each node sequentially by polling. The transmission processing by polling can improve the transmission efficiency.
Even a configuration for carrying out the access control by polling poses the problem of a deteriorated transmission efficiency in the case where transmission units (nodes) in the network increase in number. Specifically, as long as the number of nodes in the network is small, all the nodes can be polled sequentially without any serious problem. Assuming that a multiplicity of nodes exist within a network and only a small number of them have transmission data, however, the amount of polling the nodes having no transmission data increases and only many control signals for polling are transmitted. Thus, the transmission efficiency of the network is lowered, and the root node is required to transmit a multiplicity of control signals for polling, thereby imposing a heavy burden on the root node.
In the case where the nodes in the network are portable, on the other hand, the root node is required to manage the movement of the nodes. Therefore, each node is required to send a signal in response to the polling by the root node. With a configuration in which a response signal to the polling is required to be sent back always, even the nodes having no transmission data always require the communication processing for responding to the polling, thereby increasing the power consumption of each node.
An object of the present invention is to efficiently control the communication within a network system by a control station.
According to one aspect of the invention, there is provided a communication control method in which a management data transmission area is set in a frame period, a plurality of slots are arranged in the management data transmission area, and a plurality of communication stations or a control station are adapted to transmit individual data on the communication condition of the respective station in the respective slots.
The communication control method according to the present invention makes it possible to collect data on the communication conditions in each communication station for the communication using the management data transmission area.
According to another aspect of the invention, there is provided a transmission unit comprising a receiving means for receiving signals transmitted from other transmission units in respective slots set within the management data transmission area and a transmission means for transmitting the data concerning the receiving conditions of respective slots in the receiving means from predetermined ones of a plurality of slots as data concerning the receiving conditions.
With a transmission unit according to the invention, signals can be processed for receiving from other transmission units and the data concerning the communication conditions can be processed for transmission based on the receiving conditions of the received signals using the management data transmission area.